The surging temperatures led to a loss of over 40 trillion litres of water, around 10 trillion gallons, in the Colorado River Basin from 2000 to 2021, a news study published in the American Geophysical Union’s Water Resources Research has said. The loss is equivalent to about equal to the entire storage capacity of Lake Mead, the largest reservoir on the Colorado River.
The study modeled the humans’ impact on hydrology in the region.
The Colorado River Basin runs through seven Western states, covering about 647,500 square kiometres, and around 40 million people depend on it for drinking and irrigation water.
Without the effect of the climate change, the basin’s drought would not have reduced reservoir levels in the year 2021 to such a low which prompted supply cuts under the “first-ever federally declared water shortage”, the study said.
Lead author of the study Benjamin Bass said while it was known that warming was having an impact on the basin, the findings of the study were surprising. “The fact that warming removed as much water from the basin as the size of Lake Mead itself during the recent megadrought is a wakeup call to the climate change impacts we are living today,” he added.
The regional drought commenced in about 2000 and is reportedly the driest period seen in 1,200 years. It has reduced river flow and shrunk reservoirs.
The study looked into how the basin’s hydrology changed between 1880 and 2021 using a land surface model capable of analyzing water, changes in vegetation and vegetation’s response to increasing atmospheric carbon dioxide.
Researchers saw that from 1880 to 2021, the temperature in the Basin warmed about 1.5 degree Celsius due to anthropogenic climate change. “This warming has led to a 10.3% reduction in runoff in under present-day conditions. Without including the effects of plants, present-day water loss would be closer to 13%, pointing to the importance of including vegetation processes in water modeling,” the authors said.
The study also found that regions of the basin which are usually snow-covered in winter are losing water about twice as fast as typically snowless regions.